[PATCH 5.18 006/231] x86/xen: Use clear_bss() for Xen PV guests

Greg Kroah-Hartman
2022-07-19T12:51:05Z

From: Juergen Gross <jgross@suse.com>

commit 96e8fc5818686d4a1591bb6907e7fdb64ef29884 upstream.

Instead of clearing the bss area in assembly code, use the clear_bss()
function.

This requires to pass the start_info address as parameter to
xen_start_kernel() in order to avoid the xen_start_info being zeroed
again.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20220630071441.28576-2-jgross@suse.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/include/asm/setup.h | 3 +++
arch/x86/kernel/head64.c | 2 +-
arch/x86/xen/enlighten_pv.c | 8 ++++++--
arch/x86/xen/xen-head.S | 10 +---------
4 files changed, 11 insertions(+), 12 deletions(-)

--- a/arch/x86/include/asm/setup.h
+++ b/arch/x86/include/asm/setup.h
@@ -132,6 +132,9 @@ void *extend_brk(size_t size, size_t ali
}

extern void probe_roms(void);
+
+void clear_bss(void);
+
#ifdef __i386__

asmlinkage void __init i386_start_kernel(void);
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -421,7 +421,7 @@ void __init do_early_exception(struct pt

/* Don't add a printk in there. printk relies on the PDA which is not initialized
yet. */
-static void __init clear_bss(void)
+void __init clear_bss(void)
{
memset(__bss_start, 0,
(unsigned long) __bss_stop - (unsigned long) __bss_start);
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1183,15 +1183,19 @@ static void __init xen_domu_set_legacy_f
extern void early_xen_iret_patch(void);

/* First C function to be called on Xen boot */
-asmlinkage __visible void __init xen_start_kernel(void)
+asmlinkage __visible void __init xen_start_kernel(struct start_info *si)
{
struct physdev_set_iopl set_iopl;
unsigned long initrd_start = 0;
int rc;

- if (!xen_start_info)
+ if (!si)
return;

+ clear_bss();
+
+ xen_start_info = si;
+
__text_gen_insn(&early_xen_iret_patch,
JMP32_INSN_OPCODE, &early_xen_iret_patch, &xen_iret,
JMP32_INSN_SIZE);
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -48,15 +48,6 @@ SYM_CODE_START(startup_xen)
ANNOTATE_NOENDBR
cld

- /* Clear .bss */
- xor %eax,%eax
- mov $__bss_start, %rdi
- mov $__bss_stop, %rcx
- sub %rdi, %rcx
- shr $3, %rcx
- rep stosq
-
- mov %rsi, xen_start_info
mov initial_stack(%rip), %rsp

/* Set up %gs.
@@ -71,6 +62,7 @@ SYM_CODE_START(startup_xen)
cdq
wrmsr

+ mov %rsi, %rdi
call xen_start_kernel
SYM_CODE_END(startup_xen)
__FINIT